1. Field of the Invention
The present invention relates to a method of fabricating barrier ribs in a plasma display panel enabling to form barrier ribs of high precision and resolution for a large screen using photosensitive glass powder.
2. Background of the Related Art
Generally, a plasma display panel (hereinafter abbreviated PDP) is manufactured by arranging cathode and anode electrodes between a pair of glass substrates confronting each other to cross each other, injecting a discharge gas between the substrates, and sealing the substrates. PDP displays a predetermined image by applying a predetermined voltage between the cathode and anode electrodes so as to bring about gas discharge at a crossing of the electrodes. PDP has been used for a monitor of OA appliance. Lately, many efforts are made to apply PDP to the wall-hanging TV and the next generation HDTV and the like with colorization. Compared to LCD, PDP provides a large-scaled screen with ease so as to expand to be applied to various fields such as various displays and the like.
FIG. 1 illustrates an AC type PDP which is widely produced.
Referring to FIG. 1, PDP includes a pair of glass substrates. In this case, a front glass substrate is called a front substrate and the other glass substrate at the rear of the front substrate is called a rear substrate 2.
On the front substrate 1 of the AC type PDP, formed are transparent electrodes 3 for discharge and bus electrodes (attached to the transparent electrodes) to reduce line resistance of the transparent electrodes 3 by bringing about discharge opposite to the transparent electrodes 3.
And, a transparent dielectric layer 4 and a protecting layer 5 to protect the electrodes are formed on the front substrate 1. The protecting layer 5 maintains a discharge state by releasing electrons during discharge so as to control an excessive discharge current. On the rear substrate 2, barrier ribs 7 as partition walls to provide discharge spaces are formed like stripes over data electrodes 6 for writing. Inside each of the discharge spaces, fluorescent layers 8 of RGB three colors are arranged regularly for luminescence and colorization of visible rays.
The front and rear substrates 2 are bonded together by a seal layer. After maintaining a vacuum state between the substrates, a gas is injected between the bonded glass substrates so as to generate ultraviolet rays during discharge. A mixed gas such as He+Xe or Ne+Xe is mainly used for the injected gas. Modules such as driver IC and the like are installed at the above structure, thereby completing the AC type PDP.
In the AC type PDP, the barrier ribs 7 secures discharge spaces, prevents the 3-colored fluorescent layers 3 from being mixed each other, and prevents electric and optical crosstalk between discharge cells. Therefore, the barrier ribs 8 become an important factor to increase display quality and luminescence efficiency. As a panel requires large scale and high precision and resolution, many efforts are made to study the barrier ribs.
In order to fabricate the barrier ribs, there are screen printing, sand blasting, additive method, LTCCM (low temperature cofired ceramic on metal) which is used embossing, and the like.
Screen printing carries out the steps of screen-printing a rib material and drying the printed rib material 8 to 10 times so as to stack the rib material up to a designed height. After printing the rib material, a next layer is printed thereon during a natural drying process before the previously printed rib material fails to be dried up. Thus, it is very important haw far the printed rib material runs dry. Screen printing has advantages such that a screen printer is not expensive and that the material is not wasted. Namely, the rib material is printed on the designed spots only. Yet, it is very difficult to make the heights of the respective ribs uniform due to a number of printings. Besides, the pattern of the ribs fails to meet the requirement of the product such as high precision and fine resolution.
Originally, sand blasting is used for engraving letters on a tombstone or sculpturing a glass, in which sands are jetted on a stone so that the frictional energy of the sands carves the stone. Sand blasting enables to form a micro pattern using photolithography as well as form the ribs on a large-scaled substrate. Yet, sand blasting fails to prevent cracks in the glass substrate due to the impact of an abradant thereon.
In the additive method, a photoresist film is attached on a glass substrate, and exposure and development are carried out on the photoresist film so as to leave portions of the film between patterns which will become the ribs. A rib material charges the spaces and runs dry. After removing the photoresist film, the rib material is plasticized so as to complete the ribs. Such an additive method requires no sand blaster, thereby preventing massive dusts. And, the additive method is suitable for forming the ribs on a large-scaled substrate. Yet, the additive method has difficulty in separating the photoresist from a glass paste so as to leave residues. Besides, the barrier ribs may collapse during formation.
And, compared to other methods, LTCCM has a simple process.
FIG. 2A to FIG. 2H illustrate a process of fabricating barrier ribs using LTCCM.
Referring to FIG. 2A, a green sheet 30 is prepared. The green sheet 30 is prepared by putting a slurry, which is formed by mixing glass powder, organic solvent, plasticizer, binder, additive and the like together with a predetermined ratio, on a polyester film, forming the slurry as a sheet figure by doctor blade, and carrying out a drying process thereon. A substrate 32 to which the green sheet 30 is bonded is formed of metal such as titanium. Titanium is superior to glass or ceramic material in degree of strength and thermal resistance, thereby enabling to be prepared thinner than the glass or ceramic materials as well as reduce thermal and mechanical distortion.
Referring to FIG. 2C, glass powder, which is grinded finely and dried, is sprayed on the metal substrate 32 and dried before bonding the substrate 32 and green sheet 30 together so as to ease the conjunction between the metal substrate 32 and green sheet 30. The sprayed fine glass powder is melted to be adsorbed on a surface of the substrate 32 by heat treatment at 500 to 600xc2x0 C.
Referring to FIG. 2C, the green sheet 30 is bonded to the substrate 32, on which the glass powder is adsorbed, by lamination.
Referring to FIG. 2D, address electrodes 2 are patterned on the green sheet 30. The green sheet 30 is then dried.
Referring to FIG. 2E, dielectric slurry is printed on the substrate 30 on which the address electrodes 2 have been formed. And, the dielectric slurry is dried. Thus, an electrode passivation layer 36 is formed. After the formation of the electrode passivation layer 36, a second laminating is carried out so as to increase adhesiveness between the electrode passivation layer 36 and the green sheet 30 having the address electrodes 2.
In order to increase liquidity of the green sheet 30 bonded to the substrate 32, the substrate is heated at a temperature below a softening point of the organic material used as a binder.
Referring to FIG. 2F, the green sheet 30 of which liquidity is increased is aligned on a metallic pattern 38 having grooves 38a which have counter-figures of barrier ribs to be formed.
Referring to FIG. 2G, the metallic pattern 38 is pressed by a pressure over 150 Kgf/cm2 so that the green sheet 30 and electrode passivation layer 36 fill the grooves 38a of the metallic pattern 38.
Referring to FIG. 2H, the metallic patter 38 is separated from the green sheet 30 and electrode passivation layer 36. Barrier ribs are then formed through heating-maintaining-cooling steps.
LTCCM has an advantage of forming the barrier ribs with ease. Yet, LTCCM has difficulty in selecting a composition of a green sheet enabling to lower the metallic pattern pressure for the formation of the barrier ribs. Besides, the heights of the respective barrier ribs become irregular if the metallic pattern pressure forced on the substrate is not even. Hence, LTCCM requires an extra grinding process to secure the uniform heights of the respective barrier ribs.
Proposed for forming the barrier ribs are LIGA (lithography +electroplating +molding), anistropic silicon etch, photosensitive glass substrate etch, and the like.
LIGA is carried out by changing property of a portion of a resin material to which an X-ray generated from an accelerator is applied and removing the irradiated portion by etch. The structure is constructed by such a manner. In certain case, the structure is formed as a first metallic pattern. A second metallic pattern is formed by pouring a liquid plastic on the first metallic pattern. And, electroplating is carried out on the second metallic pattern so as to construct a designed final structure. Yet, LIGA requires an expensive X-ray generator.
Anisotropic silicon etch is a method of forming a micro structure using a characteristic that a Si[110] substrate has a priority in etched in a vertical direction. Yet, anisotropic silicon etch has difficulty in forming micro structures such as barrier ribs on a large-scaled surface as well as using expensive single-crystalline silicon.
Photosensitive glass substrate etch is originated from Dalton who has found the phenomenon that Cu shows a Ruby color owing to extraction after heat treatment by the reduction of Cu particles. Photosensitive glass experiences a selective crystal growth by metal particles after over-run. Photosensitive glass includes LAS (lithium alumina silicate) based glass containing Ag, to which Ce is added to increase photosensitivity.
FIG. 3A to FIG. 3D illustrate cross-sectional views of etching a photosensitive glass substrate.
Referring to FIG. 3A, a mask pattern 44 is formed on a photosensitive glass substrate 42. The photosensitive glass substrate 42 mainly consists of SiO2 and LiO2 to which CeO2, Al2O3, and a small amount of AgCl and K2O are added.
Referring to FIG. 3B, exposure is carried out on the substrate by a light source generating UV-rays having a predetermined wavelength. Thermal treatment is then carried out on the substrate.
Referring to FIG. 3C, through such thermal treatment, lithium metasillicate grows from the exposure portion 46a of the glass substrate.
Referring to FIG. 3D, wet etch is carried out on the exposure portion 46a, where crystalline phase is extracted, by dipping the substrate in a solution containing HF for a predetermined time. The exposure portion 46a where the crystalline phase is extracted differs from the non-exposure portion 46b in the state of LiO2xe2x80x94SiO2 chains, thereby being etched abruptly.
Unfortunately, the photosensitive glass substrate etching method has difficulty in preparing a large-scaled photosensitive glass substrate having a bulk type glass composition of soda-lime as well as repeating thermal treatment and etch for sufficient extraction of the crystalline phase.
Accordingly, the present invention is directed to a method of fabricating barrier ribs in a plasma display panel that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of fabricating barrier ribs in a plasma display panel enabling to form barrier ribs of high precision and resolution for a large screen using photosensitive glass powder.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method of fabricating barrier ribs in a plasma display panel according to the present invention includes the steps of preparing photosensitive glass powder by reducing a photosensitive glass material to fine powder, putting the photosensitive glass powder or the photosensitive glass powder mixed with a UV-ray transmitting organic material in a mold, aligning a photomask over the photosensitive glass powder and carrying out exposure thereon, carrying out first and second thermal treatment on the photosensitive glass powder so as to generate different crystalline phases at exposed and non-exposed portions, respectively, and forming barrier ribs by etching the portion where the crystalline phase is generated. Thereafter, glass ceramic which having barrier rib shape is adhered to Aluminum plate by using a thermal-conductive polymer (ex. Dowcorning 4173A) to improve thermal-defect and external impact strength.
In another aspect of the present invention, a method of fabricating barrier ribs in a plasma display panel includes the steps of preparing photosensitive glass powder by reducing a photosensitive glass material to fine powder, putting the photosensitive glass powder in a predetermined mold, aligning a mask pattern over the photosensitive glass powder and carrying out exposure on the photosensitive glass powder, carrying out a first thermal treatment on the photosensitive glass powder so as to generate a crystalline phase at either an exposure portion or a non-exposure portion of the photosensitive glass powder, and forming barrier ribs by etching the portion where the crystalline phase is formed.
In a further aspect of the present invention, a method of fabricating barrier ribs in a plasma display panel includes the steps of preparing photosensitive glass powder by reducing a photosensitive glass material to fine powder, printing a paste formed of the photosensitive glass powder and an organic material on a substrate and drying the paste, aligning a photomask over the dried paste and carrying out exposure on the dried paste, carrying out a first thermal treatment on the exposed paste so as to generate a crystalline phase at either an exposure portion or a non-exposure portion of the exposed paste, and forming barrier ribs by etching the portion where the crystalline phase is formed.
Accordingly, a method of fabricating barrier ribs in a plasma display panel according to the present invention requires no green sheet of which selection for a composition ratio is difficult in LTCCM, and enables to form micro barrier ribs using simple processes such as exposure and wet etch without causing any problem such as pressure concentration using a metallic pattern or uneven heights of the respective barrier ribs.
Moreover, a method of fabricating barrier ribs in a plasma display panel according to the present invention, which uses finely-reduced powder of photosensitive glass, enables to prepare a photosensitive glass plate with ease, extract crystalline phases, and reduce thermal treatment and etch time for extracting the crystalline phase sufficiently.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.